Various electronic devices are constructed of semiconductive materials. In the fabrication of such devices, insulating materials, such as dielectric materials, may be formed on surfaces of the semiconductive materials.
Dielectric coatings can be applied using electrodeposition (ED). During aqueous electrodeposition, electricity flows through the material being coated (electrode) and attracts charged particles which are dispersed in the electrodeposition bath. At the surface of the material being coated, electrolysis of water occurs. If the material being coated is serving as the anode, protons are formed at the surface which will then react with negatively charged coating particles (anodic ED). If the material being coated is serving as the cathode, hydroxide ions are formed at the surface which will then react with positively charged coating particles (cathodic ED). If electricity flows easily through the electrode (conductive material), the process is more efficient (i.e., there is more deposited film for a given set of coating conditions) than for a semiconductive or weakly conductive material.
For cathodic ED, the positively charged paint particles are neutralized by the hydroxide ions at the surface, causing the particles to become insoluble in water and collect on the surface of the cathode. The neutralized particles then coalesce into a continuous film on the surface forming an insulating layer. As the insulation increases, electrodeposition gradually decreases and then (eventually) stops.
Electrocoating has the ability to completely coat all kinds of components (inside and out) that conventional spray/brush processes cannot. It also has the potential to coat much different geometry including parts with acute angles, small holes, and sharp edges. Sharp edges have a naturally higher potential to attract charged coating particles than flat surfaces. Thus, sharp edges tend to have a higher “wet film” build than the neighboring flat surfaces. However, surface tension effects tend to pull the coating away from the sharp edge(s) during flow/cure. In addition, surface tension varies from substrate to substrate. Higher coating thickness will tend to help ensure that the edges will maintain some coverage. Higher film thicknesses on the sharp edges of conductive substrates can easily be obtained with commercial ED coatings due to the efficient flow of electricity with these substrates. The result is sufficient edge coverage. However, since semiconductive and weakly conductive substrates have greater difficulty building thicker films, these substrates may not obtain sufficient edge coverage with standard E-coats.
There is a need for a conformal dielectric coating that can form an insulating layer that adequately insulates semiconductive materials.